Download Several unsolved problems existin connexion with this (3) Why does

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VISUAL PROTECTION
IN
AERIAL WARFARE
689
to the optic nerve as possible. In any case. there is a great probability that almost half the visual field would be lost. When the
angioma is to the temporal side of the optic disc-macular vision
would be destroyed. Better that, however, than loss of the eye.
Several unsolved problems exist in connexion with this
condition (1) Is there a tendency for new angiomata to form as occurred
in one case mentioned and illustrated by Elwyn4 ?
(2) Hard white exudates may be present early as in the right
eye of case 1 described, long before any detachment was suspected.
Are these due to haemorrhage in one whose retinal vessels are
especially prone to leak?
(3) Why does retinal detachment occur when there is
apparently little subretinal exudate and no hole in the retina?
BIBLIOGRAPHY
1. MOORE. R. F,-Trans. Ophthal. Soc. U.K., Vol. LV, p: 3, 1935, Proc. Roy. Soc.
Med., Vol. XXVI, p. 1036, 1932.
2. McDONALD, R. and LIPPINCOTT, S. W.-Arch. of Ophthal., Vol. XX, p. 958,
1938.
3. NICOLL and MOORE.-Brit. Jf. Ophthal., Vol. XVIII, p. 454, 1934.
4. ELWYN, H.-Diseases of the Retina, London, pp. 169, 177, 1948.
5. WEVE, H.-Trans. Ophthal. Soc. U.K., Vol. LIX, p. 43, 1939.
6. MICHAELSON, I. C.-Brit. Jf. Ophthal., Vol. XXVIII, p. 522, 1944.
7. GOLDMANN, H.-Ophthalmologica, Vol. XCVI, p. 90, 1938.
8. FOSTER, J.-Brit. Jf. Ophthal., Vol. XXXII, p. 83, 1948.
VISUAL PROTECTION IN AERIAL WARFARE
BY
Air-Marshal P. C. LIVINGSTON
INTRODUCTION.
IN order that men may bear weapons with success and fortitude
in modern warfare, it is necessary that they be armed, not only
with equipment suitable to the occasion, but with their minds
prepared for such high adventure that the capacity for imagination is locked within the lower levels of consciousness. Throughout the World War, 1939/45, personal experience records no case
where a member of aircrew became obsessed by a dread of blindness through enemy action. On the contrary, the destruction of
sight appeared so little feared, that difficulty was experienced in
persuading personnel of the Air arm to take reasonable precautions
against ocular injury. This negation of the thought of blindness
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6906P. C. LIVINGSTON
no doubt results from the acceptance of sight as a natural
attribute, so much part of human structure that the catastrophe
of its loss is beyond contemplation. Therefore, in the heat of
action, it seems unthinkable that vision should be destroyed, leaving defenceless the combatant so afflicted. The very position of
Man in the Universe signifies that tdie guiding hand which has
led him safely through many hazards to his eventual goal, is
dominated by a broadening mind reacting to impressions transmitted through the visual apparatus.
GENERAL CONSIDERATION.
In times of conflict it becomes necessary to introduce equipment
aimed at the preservation of sight, without however creating a
state of eye consciousness among those for whom the protective
measures are intended. In lectures and demonstrations directed
to this end, the audience should be regarded as containing a group
of personnel who previously have given little thought to the risks
to vision associated with aerial warfare, but are in fact
strongly susceptible to suggestion. It becomes necessary therefore to exercise care in preserving the morale of aircrew personnel.
Other difficulties occur peculiar to this branch of preventive
medicine. No order exists- wnicn demands that aircrew personnel
shall, under threat of penalty, adopt some special precaution
designed for their safety. They may be called upon to carry a
device with them on operational duty, but there is no guarantee
as to its use. The problem becomes one of appeal to reason backed
by sound argument. In this, as in so many other matters, the
example set by Captains of aircraft becomes of particular significance. Aircrew are often hero worshippers. Frequently without
a thought, they accept as indisputable the opinion of one well
reputed for skill in combat. At times a situation so created maynot be directed to the best interests of the Service, because some
pilots of high achievement are individualists whose ideas do not
conform to the recognised tactics of combat. It should fall to the
lot of those whose duty it is to reduce wound incidence to offer
their knowledge and experience in a manner which will create a
proper understanding of the situation and of the elementary
principles concerned. It is well appreciated that great individualists in War are not always the most suitable guides for a
population so varied in background and psychological structure
as that prevailing in aircrew. These features are stressed because
they reveal a number of difficulties that may impede the use of
apparatus constituting part of a campaign directed against
traumatic' blinding.
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VISUAL PROTECTION IN AERIAL WARFARE
691
EVENTS WHICH THREATEN BLINDNESS
Some operations of aerial warfare contain hazards common to
combatant forces in general, others are peculiar to actions develop.
ing at altitude. Examples of the former are found i-n low level
attack on enemy transport columns, railway systems or airfields.
Here the defensive fire is commonly from machine guns, rifles
and other light weapons.
High level operational flying draws fire from defensive weapons
on the ground, such as light or heavy anti-aircraft guns and
rockets, while in addition attack by machine gun or cannon fire
may come from intercepting aircraft. Ocular injuries are found
to occur from missiles intact, from fragments of these after
explosion outside or inside the aircraft, or from shattered parts
of the. aircraft. Injuries of serious character are sustained through
burns from fires started in fuel tanks or by the ignition of
incendiary bombs carried within the aircraft. Fires following a
crash on landing at base sometimes occur. A forced landing as
a result of engine failure accounts for other forms of injury, as
when the head strikes against projecting parts of the instrument
panel, especially if the harness designed to restrain forward propulsion of the body happens to break.
Sudden structural failure of the air frame, in high speed
manoeuvres, when for example portions of the engine cowling
break away or a wing fractures, may terminate in severe facial
injury involving the eyes. More rarely, wild fowl have been
known to smash through the cabin structure and destroy vision.
The foreign bodies responsible for ocular injury sustained on
flying duty may be metallic or non metallic. The metallic foreign
bodies are more frequently non magnetic than magnetic. Therefore, the magnet in the extraction of these particles is of limited
value. Experience tends to show that the eye is more tolerant
of the presence of fragments of metallic alloys than was at first
believed. An exception is copper.
Perspex, one of the cellulose acetate group of materials used
in aircraft cabin windows, is fortunately very well tolerated. It
sometimes occurs that twenty or more tiny pieces of perspex
become embedded in the cornea and remain without serious
reaction occurring. The only unpleasant sequel is the abnormal
dispersion when light strikes the surfaces of these translucent
foreign bodies set at varied angles in the substance of the cornea.
METHODS OF COMBATING OCULAR INJURY
These group themselves under three headings:
(1) Measures incorporated within the structure of the aircraft.
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P. C. LIVINGSTON
692
(a) Bullet proof glass is constructed in layers united under pressure
and held together by an. adhesive substance. The glass plates
so prepared attain a thickness of 1l" or more. Welded steel or
light alloy tubing comprise the supporting framework. Illustrations 1 and 2 show the effect produced upon the front screen
of a fighter aircraft by the impact of a bullet at close range. Only
a very few flakes have been detached on the side of the screen
ILLUSTRATION 1
Front surface of bullet proof glass
windscreen, fighter aircraft showing
effects produced by 0 303 armour
piercing bullet at 200 yards.
ILLUSTRATION 2.
The same windscreen as (1), showing
surface towards pilot. Note how few
particles of glass have been shed from
the mass of cracks.
next to the pilot. (2) This effect was produced by a 303 W. Mark 1
armour piercing bullet with a charge giving an equivalent range
of 200 yards. A further example of the resistance of bullet proof
glass is illustrated (3) in the case of a bomber aircraft. This sheet
was situated behind the pilot, on the starboard side. The
photograph is taken looking aft. The attack was made by a
Messerschmitt 210 whilst the Lancaster was on a mission to
Frankfurt The aircraft received 80 hits. Of these two 792 mm.
armour piercing bullets from dead' astern and level, entered the
rear end of the cockpit canopy on the starboard side shattering
the 3" bullet proof slab. In this instance a cavity of approximately I" deep was made in the steel defence armour, positioned
behind the pilot. A further illustration (4) provides an example
of the devastating effect of close range night fighter fire upon the
rear turret of a bomber aircraft. Protection in respect of the
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l/
693
VISUAL PROTECTION IN AERIAL WARFARE
gunner's turret is of necessity less complete than in the case of
the pilot's cockpit, owing to the need to provide an observation
post which permits a good area of search. There are a number of
metal supports which offer secondary protection; but the fact that
the turret is designed to rotate, exposes the gunner in a more
vulnerable manner than is the case with other occupants of the
aircraft. Furthermore, in order to obtain the best conditions of
ILLUSTRATION 3.
Bullet proof glass screen situated behind pilot of Lancaster III aircraft.
Effect produced by 792 mm. armour piercing bullets.
visibility it became necessary to remove part of one of the perspex
panels so as to provide an avea through which search of the
night sky could be made with full freedomi.
(b) The use of armour is restricted by its weight. It affords
excellent protection for the pilot. These plates are usually 12'mm.
thick. They can resist a 20 mim. shell unless struck point on.
Their value in visual protection is indirect. For example, they
stop the flight of an explosive cannon shell, which unimpeded
might come at a narrow angle from behind the pilot and exploding against the instrument panel, scatter at high velocity'many
particles of varied composition likely, to endanger the eyes.
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694
P. C. LIVINGS1 ON
(2) Equipment in the form of goggles, spectacles, visors and
contact lenses worn by aircrew. (a) All safety glass used in
goggles is of the laminated form, that is, two sheets of glass connected by a flexible interlayer. It will be observed, in illustration
(5) d to g, that goggle windows are composed of two surfaces
meeting at an obtuse angle. This design was adopted in order
to achieve great strength. It has been shown that curved safety
ILLLTSTRATION 4.
Rear turret of Stirling aircraft after raid on Duisberg, April, 1943, showing
severe damage to the rear gun tur-ret and controls. This aircraft succeeded1
in reaching base.
glass as used in, some types of goggle~is not fully reliable. The
principle of resistance to fract'ure is founded'upon a precise union
between surfaces. This union at the present time, can only be
assured if the surfaces are flat. The specification under which
goggle glass is passed as suitable is exacting, because the optical
properties must be 'considered, as well as the safety factor.
The test for splintering is made after accelerated ageing tests in,
which the glass,is subjected to low temperature, hot moist air
and ultra-violet light. For the -splintering test, designed to
eliminate glass which on fracture has a tendency to fly, the sample
is held vertically and is struck centrally on one of its faces with
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VISUAL PROTECTION IN AERIAL WARFARE'
695
4*cd
cd
4-4
C)d
C))
,C
4*)
C)d
C)
~
~
~
-C)
d c
Cl Dc
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696
P. C. LiviNGSTON
a steel ball. Fragments which may' be split from the other
surface are collected on a lanoline treated body- placed a short
distance away. The sample is rejected if splinters are found
adhering to the lanoline. Great difficulties were encountered
during the development of safety goggles. The design even now
is not settled. Flying goggles must be light and fit comfortably.
They should not become fogged during the rapid changes in
atmosphere frequently encountered at high altitude. The provision of a wide field of view is an essential requirement. It is
important to provide protection against fire. Finally, the goggle
must be of such shape as not to interfere with the fit of the flying
helmet and oxygen mask. An idea of the work of development
necessary in order to attain a satisfactory appliance is expressed
in illustration (5) which from d to g shows some of the steps in
design. The weight of goggle d was 71 ounces, while that of
goggle g was 4 ounces. Not only is a heavy goggle uncomfortable to wear on the ground; but it is also far more handicapping
in certain manoeuvres in flight. During a sharp pull out from
a dive, the weight of,a goggle may, for a few seconds, be increased
by as much as fivefold and become displaced. As the weight
factor is extremely important, an attempt was made to distribute
pressures over the head from before backwards. The results
shown at illustration (5), (a) proved unstable in wind. Masks
such as (b) and (c) composed of synthetic material scratch too
readily. Goggles of any form are not popular in aircraft with
completely enclosed cabins, but are essential in some elementary
training aircraft, and also in certain fighter aircraft, when the
hood is moved to the open position for take off and landing.
On occasions, a goggle has proved of value on abandoning the
aircraft.
It has become necessary to provide safety spectacles of the type
seen at (5), h, j and k. The spectacles are of two types, one
intended for protection against glare (j), the other (k) for holding
corrected lenses in the case of defective visual acuity. In order
to provide a field of acute vision as wide as possible, it is necessary
that tWe frames designed to hold correction fit close to the eyes.
The lenses must be ground large. The measurements of the
corrected safety lenses illustrated are 44x50 mm. It is also
necessary to provide a type of fitting which will maintain the
spectacles in position in the presence of strong wind. The side
pieces, therefore, are of metal closely applied to the sides of the
head. An alternative fitting is provided which permits an elastic
strap to be attached to the outside of the flying helmet.
(c) Visors made of synthetic material have been a source of
experiment. Two factors, however, militate against favourable
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VISUAL PROT'ECTION IN AERIAL WARFARE
697
results; namely the softness of the substance, thus causing a reduction in visual acuity owing to the rapid appearance of multiple
scratches and the difficulty in obtaining the material suitably
tinted to ward off sun glare direct or reflected. It is also to be
observed that the synthetic substances of the cellulose acetate
group permit the unimpeded passage of ultra-violet light in
contra-distinction to the properties of glass. The advantages of
visors of this character are that they are light and can readily be
moulded to fit the curves of the head and the contours of equipment. Visors are illustrated at (5) b and c, with tinted shields
attached.
(d) The employment of contact lenses is limited by the intolerance from ocular sensitivity, of about 60 per cent. of those who
undergo preliminary trials with the shells which are employedc
in the first instance. They are of great value in the few instances
in which tolerance exceeds seven hours. They are strong and
very resistant to fracture owing to the elasticity of the orbital
content against which they are forced in the event of a blpw.
(3) Methods adopted to increase visual perception.-An
indirect but highly important method of aiding visual protection
is to build up a system of instruction with the idea of quickening
visual percepiion, thus raising the speed of detection and recogni-.
tion of aircraft by day or night. The greatest attention has beerl
ILLUSTRATION 6.
A gymnasium used for night vision training. Note the black and white
painted hoops and skittles, as well as the white trestle used in walking
and balancing exercises under low illumination.
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'698
P. C. LIVINGSTON
given to improving performance under conditions of low illumination. The problem is complicated and the benefit gained is based
largely upon assumption without clear statistical proof.
The
basis of this form of training received strong approval at Royal
Air Force Headquarters, especially in Bomber Command.
Fighter Command developed the technique in respect of its night
fighter pilots. The aircraft were later equipped with radar for establish-ing contact with the enemy outside visual range. It was nevertheless essential for the human eye to establish identification. Night
vision training comprises lectures upon the general principles of
scanning at night time, together with practice using various
devices under conditions equivalent to moonlight and starlight.
Demonstrations are provided which show the effects created by
altering the position of the source of nigh5 illumination upon
ground targets. Games are played under low illumination in the
gymnasium as illustrated in (6) with the participators wearing
light trapped safety goggles containing dark filters. After a few
lessons the improvement in performance is often remarkable. In
the case of night interceptor pilots special care is taken to assure
a high standard of night visual capacity before flying training
in this branch of aerial warfare is commenced.
THE ASSESSMENT
OF
PROTECTIVE MEASURES
In estimating the full value of the measures which have been
described, it is found very difficult to establish the position on a'
statistical footing. So many and varied are the situations
encountered in War operations, that it is hard to discover sure
ground from which the true value of visual protection can be
calculated. For example, a number of personnel found it
impossible to wear their goggles regardless of the wide field of
vision provided and the eventual comfort attained, because they
experienced a feeling of restriction, however good the optical
qualities of the goggle glass. Much depends upon skill in the
tactics of combat in the air which applies equally to both sides.
Much of this skill is founded upon experience, with which goes
a greater capacity for accurate and rapid visual perception. The
element of fortune tends to exercise a strong influence upon the
issue. It is, in truth, only possible to institute a search for various
ways of protecting the eyes against injury, to employ every one
that appears practical and likely to be appreciated, to spare no
pains in explaining the value of these procedures, so that the
greatest number of personnel will be encouraged to make use of
them, and from this position to await the issue. One positive
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699
VISUAL PROTECTION IN AERIAL WARFARE
approach in the campaign against blindness is the early elimination or treatment of those of doubtful visual capacity for day or
night flying duties. At one time it was necessary to accept pilots
with a visual acuity no better than 6/18 in both eyes correctable,
however, at least to 6/6. To assist these personnel, over 12,000
goggles with correcting lenses were issued. The high standard
of at least 6/6 in one eye and not worse than 6/9 in the other,
was maintained-for Air Gunners and Bomb Aimers. Over 200,000
tests for night visual capacity were carried out, with a rejection
rate that rose to over q per cent.: At the same time care was taken
to observe personnel who were of borderline category in th-is
respect, and have them sent to a special clinic if their performance in the air at night was adversely reported by the Captain
of the aircraft. In this manner, in one year, over one hundred
personnel were subjected to a careful examination in which the
field of niight vision was studied by means of self luminous targets,
and eliminating action taken when field defects were discovered.
Among such personnel were those who suffered from early retinal
Ocular Injuries due to Enemy Action
3
34
,.
Perforating
Injury
26
I
I
I
Non-perforating
In jury
8
I',
Both eyes
One eye
1
7
'-
Total
blindness
Blindness of
2
17
one eye
Partial blindness
of one eye,
other eye
unaffected
I
5
Serious injury
to other eye
I
2
Slight injury
to other eye
Other eye
unaffected
2:
13
Slight defect of
vision, one eye
only
I
2
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700
P. C. LIVINGSTON
disease, or from changes reflecting themselves in the scotopic
visual field, as in diabetes.
THE INCIDENCE OF BLINDNESS IN AIR CREW PERSONNEL IN FLIGHT
The total loss of sight of both eyes has occurred twice only in
flying operations against the enemy. The after history of one
case provides a fine example of the ability of youth to surmount
this catastrophic event. Entering a University he studied law
and obtained honours at the graduating examination. The policy
which guides such cases into the care of the St. Dunstan's
organisation is, without question, right. It is here alone that a
full understanding of the psychology of blindness has been
mastered.
The table, p. 699, provides an analysis of the ocular injuries
from Royal Air Force records, confined to air engagements with
the enemy.
SUMMARY AND CONCLUSION
(1) The preservation of sight can be aided by the use of bullet
proof glass screens and armour plates fitted within the structure
of the aircraft.
(2) Further protection can be effected by equipping aircrew
with flying goggles or spectacles fitted with safety glass windows
which can be ground so as to provide correction in cases
of refractive error, or by fitting contact lenses in certain cases in
which the refractive error cannot be otherwise adequately treated.
The eyes behind contact lenses can move over a wide range without loss of acuity.
(3) Visual training offers a valuable indirect method of protection by instructing personnel in careful scanning procedure,
how to make the best use of rod vision under states of low
illumination, and quickening' the powers of recognition of the
objects detected.
(4) The,record of ocular injury sustained by personnel of the
Royal Air Force in flying operations lends weight to the belief
that a planned campaign, against the hazard of loss of sight reaps
its rewards.
[Illustrations Crown Copyright Reserved]
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VISUAL PROTECTION IN
AERIAL WARFARE
P. C. Livingston
Br J Ophthalmol 1948 32: 689-700
doi: 10.1136/bjo.32.9.689
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